Fire responsive mechanism



Sept. 1, 19534 M. F. PETERS FIRE RESPONSIVE MECHANISM Filed Dec. 30.1949 IN V EN TOR. MEL VALLE F ,DET'ER5 A T'T'OE/VEX Patented Sept. 1,1953 UNITED STATES PATENT OFFICE 6 Claims.

This invention relates to fire-responsive mechanism, and particularly tothe detection, signalling, and extinguishing of fires originating nearthe power plant or other vital part of an airplane or other automotivevehicle.

An object of the invention is to provide a hollow element formed andtreated in a novel manner enhancing its suitabilit and efficiency as afire detecting element capable of transmitting an alarm signalelectrically to one or more observation stations at a distancetherefrom.

A second object of the invention is to provide a fluid conduit equippedwith inlet and outlet points for the introduction and discharge offirefighting fluids, such as those commonly used in fire extinguishers;the said fluid conduit also serving as a fire detecting element capableof participating in the transmission of operating energy to an alarmsignal device located at a distant observation station.

A third object of the invention is to provide a novel signalling systemresponsive to the presence of fire, and characterized by the use of afluid conduit as a component part of the electric current flowcontrolling means by which the transmission of a fire alarm signal iseffected.

A fourth object of the invention is to provide electric current flowcontrolling means of novel construction, including the provision of alayer of thermistor material on the outer surface of a metallicconductor, said thermistor layer serving to resist completion of anelectric circuit therethrough in the presence of moisture, and furtherserving to accelerate completion of an electric circuit therethrough inthe presence of fire or heat of such an intensity as to signify thepresence of an elevated temperature.

A fifth object of the invention is to provide a fire-fighting fluiddistributing conduit having an outer layer of thermistor materialadapted to control electric current flow for operation of a fire alarmsignal device, and having the characteristics indicated.

A sixth object is to provide a fluid distributing conduit having a layerof thermistor material interposed between layers of metal, the innerlayer of metal serving as the basic conduit and the outer layer of metalco-operating with the thermistor layer to control .fiow of signalcurrent in the presence of fire or intense heat.

A seventh object is to provide a fluid distributing conduit having innerand outer layers of thermistor material adapted to cause completion of asignalling circuit only when the intervening metal of the conduitbecomes heated to a degree suggestive of fire.

These and other objects of the invention will be better understood uponexamination of the following description of the particular embodimentsof the invention illustrated in the accompanying drawings wherein:

Fig. 1 is a diagram illustrating a fluid distributing conduitsurrounding and supported on the casing of an internal combustion engineor other vehicle component susceptible to attack by fire;

Figs. 2 and 3 are diagrams illustrating a fire alarm signalling circuithaving a fluid distributing conduit as one of its component parts; thesaid conduit being constructed in a manner embodying the principles ofthe invention; and

Fig. 4 shows a section of a conduit constituting another form in whichthe invention may be embodied.

In Fig. 1 is shown the simplest type of thermistor fire detector, sodesigned that it may be used to distribute the carbon dioxide or otherextinguishing material. It consists of a metal tube I, the walls ofwhich may be plain, fluted, or corrugated in any common manner, and ofsufficient thickness to withstand mechanical handling. It is supportedby insulators 5. The holes 4 are so placed that when 002 enters through6, the extinguishing material will be distributed throughout theconfining chamber I. The fire signal is given when a flame 8 makescontact simultaneously with the tube I and the engine or metallic body3. The chief objection to this simple type of fire detector is that afalse alarm may be given if moisture collects on the insulation 5, orfail to give an alarm if the flame fails to contact both the tube I andthe engine 3 simultaneously.

The probability of false alarm may be great- 1y reduced by covering thesteel tube I with thermistor material 2. The tube does not becomegrounded by moisture on the insulators 5, because the thermistormaterial may be made to have a high resistance below the boiling pointof water. When the tube is heated the resistance rapidly decreases andbecomes a relative- 1y good conductor. By selecting the composition ofthe thermistor material the temperature at which the material becomes agood conductor can be controlled. The term thermistor material isintended to include any material having a negative temperaturecoefiicient of electrical resistance, such as porcelain or analagousglazing and enamelling materials. This arrangement of covering the steeltube with thermistor material has the advantages of an insulated tubewhen the detecting element is below some predetermined temperature andthe advantages of a noninsulated tube in the presence of an elevatedtemperature. It still has the disadvantage of requiring the flame tomake contact simultaneously with the steel tube I and the engine 3. Bothtypes, one without thermistor material and the second with it areessentially flame detectors, in that the flame 8, upon makingsimultaneous contact with the tube and the engine housing 3, may therebycomplete an electric circuit leading to a fire. alarm signal device,or'fire indicator, such as 'the'indicator'l3 of Fig. 2.

In Figure 2 is shown a unit which may serve in a dual capacity: first,as a heat or flame detecting unit, and secondly, as ameans-fordistribut' ing the extinguishing material. It will actuate theindicating mechanism when some portion of the tube reaches apredetermined temperature,

whether this temperature is caused by a flame or the ambient atmosphere.same as a two wire thermistor, with the added feature that theconductivity of the flame. may play animportant part in determiningtheactual'resistance between the steeltube land the metal braid 9,shown-in Figure 2. The braid may be made of round or flat wire, or maybe.-merely astrip. of tape orwire wrapped around the tube. Using thesame notationas in Figure 1, the tube is covered with thermistormaterial 2,. a. few. thousandths inch'thick, and over this is. stretchedaimetal braid-or wrapped conductor 9, which is grounded by supports Thesteel tube. 1 is connected to the CO2 or other extinguishing materialsupply tank by means of an electrically insulating coupling H Thecoefiicient of expansi-on of-themetaltube I, the thermistor material 2..andthewire braid is the same, so that when the ambient temperatureincreases moderatelyfast, the braid remains in contact with thethermistor material and the signal'is actuated by conduction from braidto; tubethrough the thermistor material. When a hot flamestrikes themetal braid it will-heat". more rapidly than the-thermistor materialand-the steel tube. Because of theunequal heating andconsequentlyunequal expansion, some. parts of thebraid will failto-makecontact with thethermistor material by a few thousandths of an.inch,.butthe flame :will complete the circuit between the braid and-thermistormaterial where this; separation ocours;

The metal braid or circumventing conductor serves as a protection forthe thermistor mate-- rial and radio shields the tube,- so that-for acheap installation the voltagefor actuating; the signal maybe'obtainedby capacitance coupling to the ignition cable without causingradio interference. Sucha signalling-unit is shown in Figure 2. Themetal tube H isslipped over the ignition cable I2. A wirefrcmthe-metaltube isconnected to one. terminal of the neon light [3' and the otherterminal is connected to the steel tube bymeans of the'conductor l5.The-condenser: I4- is connected acrossthe neonlight I3, so that thevoltage across the neon light will not be great enough tocausebreakdbwnuntilthe thermistor material becomes conducting. It'isto bepointed out thata better'type of indicator is recommended when theinstallation can stand the cost; but this indicator l3 willbe-satisfactory for a cheap installation'.

A further improvement may be obtained by using the combination shown inFigure 4. In this arrangement, t is the steel tube, 2 the thermistormaterial which is only a few thousandthsinch thick, and iron wire braidor other In principle, it: is the.

suitable metal covering 9, and IS a covering of thermistor material overthe complete unit. When a flame 8 strikes the thermistor material, asection AX is heated so that the current is conducted from the braidwire, or its equivalent, 9, to the steel tube I. This lowers theresistance and actuates the signal.

The resistance of enamel covered metal tubes to withstand mechanicalabuse at elevated temperatures, has been demonstratedby; the long lifeof exhaust stacks when covered with ceramic material. Their resistanceto mechanical abuse atlow temperatures has been amply demonstrated-bythe increased life of steel coal chutes when covered with enamel. Theseenamels are all thermistor: materials. By the use of thermistor Iintendtoincludeall enamels responding to the same law of resistance decreasewith rise in temperature.- The enamel material commonly used as acovering for kitchen pots and pans has been found to be verysatisfactory as a thermistor material, and willbesuitable for thepurposeszof the present invention; For further identification'ofthermistor materials; which are now well known, reference may be hadtomany patents. issued to Bell TelephoneLaboratories, whereinthermistorsandthermal transitors are described; one such patent beingthe Koch patent of September 19,- 1950.

The electrical resistance of. the braid over the steel tube, with a fewthousandths of thermistormaterialbetween the two, will be" many. timeslower than two wire thermistors. This means,- with the same operatingvoltage the. currents will be many times greater inthe braid-tube; typecomparedv to the two-wire type. This reduces the probability of falsealarm'by groundingdue to moisture.

The tubel may be made of steel from. thestandpoint of economy. The costof thetube. per foot will depend uponthe diameter and thickness'of thewall. The cost of covering itwith thermistor material inlargecquantities is. relatively cheap. As aconcrete example akitchenpotcovered with'an enamel which is thermis-- tor material may beproducedfonless than 25 cents. The steel braid. is cheap and: may be slippedintoplace over thetube; If it is desired. to insulate both tubeand. braid aheavy cheap. connector may be used, since resistance to ground isnotcritical. Instead ofbraid, a metal ribbon maybe wrapped around the tube.The indicators for these heat and flame detectors are similar tootherthermistor indicators. Because of. the lower resistance thecircuitconstants in the indicator would be changed. The one in Figure 2 isrecommended for cheap installation-only.

Fora cheap indicator for automotive or bus service, the; steel, tubecovered with thermistor material'shown in Figure 1, with the indicatingcircuit as'shown in Figure 2, would'suffi'ce.

The alarm control circuits maybe employed independently of the fluiddischarging feature, where the-latter is not needed. Also, if desired,

, each of the fluid discharge holes in the conduits sourcetosaid-indicator element, said electric cir- Similarly; othercuitincluding a metallic tube having a coating of thermistor material whichis a ceramic enamel and whose thickness is only a few thousandths of aninch, said coating being of high resistance at norma1 temperature andthereby preventing flow of electric current sufiicient to actuate saidindicator element, but of low resistance at abnormally high temperaturesand thereby causing flow of electric current sufiicient to actuate saidindicator element.

2. Means for indicating the presence of flames, comprising an indicatorelement, a source of electrical energy, means including an electriccircuit for delivering operating energy from said source to saidindicator element, said electric circuit including a tubular elementhaving a coating of thermistor materia1 which is a ceramic enamel ofless than twenty thousandths of an inch, and means for electricallygrounding said tubular element and coating during any period when thethermistor material is hot enough to conduct electric energy, saidgrounding means including a metallic covering surrounding said coating.

3. Means for indicating an abnormal temperature rise occurring in thevicinity of an internal combustion engine power plant having itsignition circuit enclosed in metallic shielding, comprising anindicating element and electrical connections extending from saidshielding to said indicating element, said electrical connectionsineluding a metallic element having a thin coating of thermistormaterial, which is a ceramic enamel, forming part of the path of currentflow leading to said indicating element.

4. A system as defined in claim 1, wherein the system is applied to aninternal combustion engine having electrical conductors supplyingignition current thereto, and wherein said energy source comprises theelectrical shielding encasing said conductors.

5; A fire detecting circuit including a signal element, a source ofelectric energy, a conduit having a very thin coating of thermistormaterial, which is a ceramic enamel and means for contacting saidcoating for grounding said coating when it becomes hot enough to beelectrically conductive.

6. A circuit as defined in claim 5, wherein said conduit is in the formof a tube, to facilitate flow of fire-fighting fluid therethrough.

MELVILLE F. PETERS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,493,327 Dunbar May 6, 1924 2,315,872 Kernen Apr. 20, 19432,487,526 Dahm Nov. 8, 1949 2,495,867 Peters Jan. 31, 1950

